RNC in Pool to Enhance Network Reliability Author: Hu Guang
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Introduction 1.1 Mobile Broadband Trend Smartphones are undergoing rapid development. For example, the smartphone penetration is expected to be over 50% by 2015 in Western European countries. This has been pushing data traffic into drastic increases. Furthermore, this strong momentum is still gathering. Smartphone penetration in Western European countries
Signaling flows are on fold increases as high-speed data services and smartphone applications are multiplying, generating signaling storms. The signaling connections per hour on a typical smartphone are above five times over a feature phone. This is stimulating challenging demands on processing capacity of mobile network infrastructure. In parallel, data services are contributing more profits than voice services, which once presented more profits to operators. Therefore, surging data flows are another challenge following the signaling storms.
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Service trend on smart mobile terminals
1.2 Challenge of Mobile Broadband to Radio Network Controller With continuous development of smartphone and mobile internet, higher demands of signaling and larger data traffic capacity are required to the mobile network. This sets higher demands on radio network controller (RNC) in terms of both user-plane and control-plane capacity and reliability. Traditionally, if one RNC goes faulty, all the services are interrupted on the NodeBs under this RNC. This is calling for new solution to ensure higher RNC reliability.
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Solution 1.3 Overview With the RNC in Pool solution, an RNC is additionally configured with an interface Iur-p through which several RNCs are connected to form a resource pool. The RNCs in the pool work in redundancy mode. RNC in Pool networking
On an RNC in Pool network, two or more RNCs are connected to each other through the Iur-p interface. When one RNC goes faulty, another RNC obtains the fault information through the Iur-p interface and takes over the services that are provided by the faulty RNC.
1.4 RNC in Pool High Reliability The RNC in Pool high reliability is achieved by connecting a NodeB to two or more RNCs through the Iub interface. The RNC that has the control right over dual-homing NodeBs is a primary RNC. When the primary RNC goes faulty, the RNC control right change is triggered to enable other RNCs, to which the NodeB belongs, to have the control right to restore services. This helps prevent service interruption on the network when one RNC is faulty.
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RNC redundancy on an RNC in Pool network
1.4.1
Advantages: −
The RNC ID remains the same after the RNC control right changes, freeing of configuration changes on other NEs.
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With N+1 redundancy, one RNC can work as backup for several active RNCs. This raises hardware utilization and lowers hardware bills.
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The RNCs in redundancy mode can still connect to NodeBs and provide services.
Impact: −
Dual-homing links must be configured on the Iub interface.
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Backup routes must be configured on the Iu interface.
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Backup hardware is required.
RNC Control Right Change Modes
The RNC control right change can be triggered manually or automatically. Manually triggered RNC control right change Having observed an alarm and exception and found that the RNC is faulty and an RNC control right change is needed based on the fault type and severity, a duty staff in the equipment room manually triggers an RNC control right change so that one secondary RNC takes over the control right over dual-homing NodeBs. After the RNC fault is rectified, the duty staff can manually trigger an RNC control right change again to enable the primary RNC to take back the control right over the dual-homing NodeBs.
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Manually triggered RNC control right change in an RNC in Pool network
Manually triggering is performed by the duty staff and is easily implemented. Therefore, it is helpful in the initial stage of operating an RNC in Pool network.
Advantages: −
Manual triggering helps prevent possible impact brought by automatic triggering. For example, online UEs are forcibly disconnected and single-homing NodeBs are out of service after the RNC control right changes.
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When the automatic redundancy function is enabled, manual triggering helps prevent possible impact brought by automatic triggering during such operations, such as transmission adjustment, device reset, and software upgrade.
Automatically triggered RNC control right change On an RNC in Pool network, the RNCs with the same NodeB multi-homing relationship periodically transmits heartbeat messages to each other over the Iur-p interface or over other standard interfaces when the Iur-p interface is faulty. In this way, the RNCs detect the running status of each other. If no heartbeat message or abnormal heartbeat message is detected, one secondary RNC automatically triggers an RNC control right change to take over the logical RNC to serve the dual-homing NodeBs. When the fault is rectified on the primary RNC, the secondary RNCs detect the heartbeat message. Then, the secondary RNC decides to trigger an RNC control right to enable the primary RNC to take back the control right.
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Automatically triggered RNC control right change in an RNC in Pool network
Advantages: −
An RNC control right is automatically triggered. Therefore, interrupted services can return normal in case of RNC faults caused by a natural disaster.
Impact: −
An automatic RNC control right change caused by any inaccurate detection brings about adverse impact on network performance.
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An unexpected RNC control right change may also be automatically triggered during some maintenance operations when the automatic redundancy function is enabled.
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Conclusion The RNC in Pool solution aims to improve the RNC reliability by load sharing and RNC redundancy to sustain the drastic development of mobile broadband, while increasing the capacity of a single RNC. The RNC in Pool solution provides advantages as follows:
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Each single RNC provides higher capacity, helping reducing the number of required RNCs.
The solution supports multiple logical RNCs and N+1 redundancy, helping increase hardware utilization.
The solution supports evolution to cloud-based network in terms of both hardware and software architectures.
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